This invention relates to an ignition circuit for use in an internal combustion engine.
It is well known that amount of various injurious components contained in exhaust gas of an internal combustion engine has relationship to the temperature within the cylinder of the engine. Ignition timing of the engine influences the combustion temperature within the cylinder. For example, the amount of nitrogen-oxide in the exhaust gas can be decreased by delaying the ignition timing of the engine. Various ignition circuits have been developed which delay the ignition timing depending on various operating conditions of the engine. For example, the ignition circuit is well known in which a one-shot multi-vibrator is provided for delaying the ignition timing. But such an ignition circuit has the drawback that the delay angle with respect to the crank shaft increases according to the increase of the rotating speed of the engine.
In another known circuit, there are provided two magnetos which generate alternating voltage signals having different phases from each other. These signals of the magnetos are used to determine the ignition timing of the engine. That is, a switching element is provided for selecting the signals so that spark plugs fire under normal timing when one of the two magnetos is selected, and under delayed timing when the other is selected. However, this circuit is also disadvantageous in view of its complexity and cost.